For what it's worth I also tinker with the brass shells somewhat in my Grand father's old single. I use black, card and fiber followed by the shot or slug and use a thin overshot card atop that assembly. I also have an older MEC progressive that has the metallic crimp starters and I run the finish shell into those just enough to create a fold over (actually I ought to say a crimp START.......enough to firmly hold that overshot card), six or 8 point....top it with duco and done. I have not experienced a shell loss thru splitting yet......